Most roadways or highways are provided with guardrails adjacent the roadway, particularly in dangerous areas, the guardrails serving to prevent a vehicle from leaving the right of way in the event of an accident or a loss of control. Many lives have been saved by such guardrails.
Guardrails are usually made up of longitudinally extending sections of rail mounted to generally vertical posts spaced apart adjacent the roadway. The posts are usually spaced from the edge of the road surface, usually adjacent an intervening shoulder. There may be a mounting block between the rail and the post to lesson the possibility of impact between a vehicle and a post itself. Two common cross-sections for guardrails include a hollow square or rectangular box section and a "W"-shaped section. The latter is actually closer to a pair of vertically-spaced sideways-lying shallow "V"-shaped channel section joined by a narrow central straight portion extending between the ends of adjacent legs of the channel sections. When there is contact between a vehicle and the guardrail, particularly in the vicinity of a post, each of the channel sections will act as a shock absorber as it flattens under the effects of the impact. This reduces the possibility of post breakage and helps to keep the vehicle within the roadway right of way.
In wintertime conditions large graders and trucks carrying plows are used to keep the roadway clear of snow. These plows also keep the shoulders clear and, very often, there is forceful sliding contact between the end of a snowplow blade and the guardrail. Such contact can be sufficiently great so as to deform the guardrail, much as can happen in a vehicular impact. If a deformed guardrail is later struck by a vehicle it will not be able to perform its shock absorbing function and hence there is an increased chance of vehicular damage and/or post breakage. Damaged guardrails must be replaced, at considerable expense to the provincial or state government, and hence it is very desirable to minimize the damage suffered by guardrails in non-vehicular accident incidents.